1. Field of the Invention
The present invention relates to a method of preventing polymer scale deposition on the inner wall and so forth of a polymerization vessel during polymerization of a monomer having an ethylenically double bond.
2. Description of Prior Art
In processes of preparing polymers by polymerizing a monomer in a polymerization vessel, the problem that polymers deposit on the inner wall and other parts which come into contact with the monomer such as stirring blades of the polymerization vessel in the form of scale, is known. The deposition of the polymer scale on the inner wall results in disadvantages that the yield of the polymer and the cooling capacity of the polymerization vessel are lowered; that the polymer scale may peel and mix into manufactured polymer, thereby impairing the quality of the manufactured polymer; and that removal of such polymer scale is laborious and hence time-consuming. Further, since the polymer scale contains unreacted monomer, there is a danger that the workers may be exposed to the unreacted monomer, which may give them some physical disorders.
Heretofore, there are known methods for preventing polymer scale deposition in which the inner wall and so forth are coated with various materials as polymer scale preventive agents, for example, particular polar compounds (Japanese Patent Publication (KOKOKU) No. 30343/1970); dyes or pigments (Japanese Patent Publication (KOKOKU) No. 30835/1970); particular linear or branched polyaromatic amines (Japanese Patent Publication (KOKOKU) No. 16561/1984); condensates prepared by reacting an aromatic amine compound with an aromatic nitro compound in the presence of a condensation catalyst at 100.degree. to 250.degree. C., or the basic form thereof produced by treatment with an alkali metal salt or ammonium compound (Japanese Patent Publication (KOKOKU) No. 30681/1985); and a quinone-amine compound with an average molecular weight of 3,000 or more prepared by subjecting an aromatic amine and an aromatic quinone to addition reaction in a solvent having a solubility parameter of 9.0 to 12.2 or a mixed solvent containing said solvent and an alcohol (Japanese Pre-examination Patent Publication (KOKAI) No. 7309/1986); a reaction product of a phenolic compound with an aromatic aldehyde (Japanese Pre-examination Patent Publication (KOKAI) No. 54317/1980); a reaction product of a phenol compound with an aromatic aldehyde (Japanese Pre-examination Patent Publication (KOKAI) No. 54317/1980); a self-condensation product of a polyhydric phenol dissolved in an aqueous alkali metal salt solution; a reaction product of pyrogallol with an aldehyde (Japanese Patent Publication (KOKOKU) No. 59246/1985); a reaction product of pyrogallol or a hydroxyhydroquinone with an aromatic aldehyde (Japanese Pre-examination Patent Publication (KOKAI) No. 192413/1982).
These methods are effective in preventing polymer scale deposition, in the case where the monomer to be polymerized is vinyl halide such as vinyl chloride or a monomer mixture containing a large amount of vinyl chloride and a small amount of other monomers copolymerizable therewith. However, in the case where the monomer having an ethylenically double bond to be polymerized mainly comprises styrene, .alpha.-methylstyrene, acrylate, acrylonitrile or the like, which have so high a dissolving power against the coatings formed by the above prior art methods, the coatings may be partly or completely dissolved away. Consequently, it becomes impossible to prevent the deposition of polymer scale.
There are also known methods for preventing polymer scale deposition in which the inner wall of a polymerization vessel is coated with the following compounds: a mixture of a water-soluble anionic polymeric compound (Japanese Pre-examination Patent Publication (KOKAI) No. 112903/1981); a cellulose or a cellulose derivative (Japanese Patent Publication (KOKOKU) No. 14444/1983); alginic acid or a metal salt thereof (Japanese Patent Publication (KOKOKU) No. 14445/1983); or a starch or a derivative thereof (Japanese Patent Publication (KOKOKU) No. 14447/1983). Although the coatings formed by these methods are not readily dissolved by monomers, the scale preventing effect achieved varies largely depending on the kind of monomer, suspending agent, catalyst, or the like used in the polymerization. Particularly, in the case of the polymerization of styrene, .alpha.-methylstyrene, acrylates, acrylonitrile or the like, polymer deposition is not prevented sufficiently.